We performed new diffraction experiments to clarify the equation of state (EoS) of stishovite after we suspected systematic errors in previous experimental reports. Using diamond anvil cells, we repeated both single-crystal X-ray diffraction measurements under hydrostatic conditions and powder diffraction measurements using the laser-annealing technique and NaCl pressure medium. The major improvement is the increase in precision of the pressure determination using the quartz and NaCl equations of state. Using both sets of data, the stishovite bulk moduli were refined to K0 = 309.9(1.1) GPa and K0′ = 4.59(0.23). We also reinvestigated the mechanism of the phase transformation to the CaCl2-structured polymorph of SiO2 at about 60 GPa. We confirm no volume discontinuity at the transition pressure, but the CaCl2 form appears slightly more compressible than the rutile-structured form of SiO2. This change in compression behavior is used for quantitative analyses of the spontaneous strains of the pressure-induced phase transition.

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